<jats:title>ABSTRACT</jats:title> <jats:p> We have identified a cellular factor that interacts with the virus genome-linked proteins (VPgs) of a diverse range of potyviruses. The factor, called <jats:italic>Potyvirus</jats:italic> VPg-interacting protein (PVIP), is a plant-specific protein with homologues in all the species examined, i.e., pea, <jats:italic>Arabidopsis thaliana</jats:italic> , and <jats:italic>Nicotiana benthamiana</jats:italic> . The sequence of PVIP does not identify a specific function, although the existence of a “PHD finger” domain may implicate the protein in transcriptional control through chromatin remodeling. Deletion analysis using the yeast two-hybrid system showed that the determinants of the interaction lay close to the N terminus of VPg; indeed, the N-terminal 16 amino acids were shown to be both necessary and sufficient for the interaction with at least one PVIP protein. From a sequence comparison of different potyvirus VPg proteins, a specific amino acid at position 12 was directly implicated in the interaction. This part of VPg is distinct from regions associated with other functional roles of VPg. Through mutation of <jats:italic>Turnip mosaic virus</jats:italic> (TuMV) at VPg position 12, we showed that the interaction with PVIP affected systemic symptoms in infected plants. This resulted from reduced cell-to-cell and systemic movement more than reduced virus replication, as visualized by comparing green fluorescent protein-tagged wild-type and mutant viruses. Furthermore, by using RNA interference of PVIP in <jats:italic>Arabidopsis</jats:italic> , we showed that reduced expression of <jats:italic>PVIP</jats:italic> genes reduced susceptibility to TuMV infection. We conclude that PVIP functions as an ancillary factor to support potyvirus movement in plants. </jats:p>